Selection of pillar recovery scheme under the condition of poor cemented backfill

For the filling method mine with better surrounding rock stability, the two-step mining is generally adopted, one step is first returned to the mining room, and the second step is returned to the mining column and the top bottom column. In the first step, due to the mining in the empty field, the mining process is simple, the depletion and loss indicators are easy to control, and the two-step ore is filled or surrounded by the filling body. The strength, integrity and self-supporting height of the filling body will be pillar recovery have a significant impact, this paper discusses the studs and roof-pillar mining program under the crest Tsui gold mine adverse cemented backfill.
1 mining technical conditions
The Jiguanzui gold deposit belongs to the post-magmatic high-medium temperature gas-liquid skarn type deposit. The surface of the mining area is the Weihu Lake area, with dense water networks, ditches and rivers. Mining of pillars shall not cause uneven settlement and collapse of the surface, and shall not damage the aquifer.
The ore body is controlled by structure, and the four identified ore bodies are composed of 50 large ore bodies, of which 5 are main ore bodies (I2, II2, III1, III2, III3). The overall orientation of the ore body is generally NE35°～72°, tending to NW, partial anti-dip, with gentle inclination (13°), inclination (55°) and steep inclination (83°～90°). The ore bodies are concentrated between 013-030 lines -5 to -622 m elevation, 50-350 m long, 2 to 27 m horizontal, and 30 m thick. The shape of the ore body is complex, and the phenomenon of branching and compounding is serious. It is mainly lenticular, irregular lenticular, partially cystic and irregular veins.
The surrounding rocks of the top and bottom of the ore body are mainly marble , dolomitic marble and gray dolomitic marble, and some are skarn. The ore f=6～10, medium stability; the surrounding rock f=6～8, most of which are stable and partially unstable; the boundary of the ore is clear.
2 mining status
The production scale of Jiguanzui Gold Mine is 1800-2000t/d. The mine is divided into two phases. The first-stage mining range is from -40 to -160m, and the mining has been completed. The second-stage mining range is -160~-470m. The middle section of -320m is the middle section of the first mining. And -220m middle section, and then down mining -370,-420,-470m middle section. In the middle section of -320m and the middle section of -270m, the large number of columns and top and bottom columns are not recovered after the recovery of the stope. The width of the column is generally 10-15m, and the height of the bottom column is generally 10~16m.
The existing mining methods in the mine are the segmentation empty field post-filling method and the shallow hole retention ore filling method. After the first step of mining, the graded tailings are filled with high-water cement, but the filling quality is poor and the strength is low. From the exposed high-water cemented filling body, the filling body is basically not consolidated, and it is sand-like and cannot stand on its own, which brings great difficulty to the mining of the column and the top and bottom columns.
3 column recovery plan selection
Filling method mining columns mainly include layered filling method and stage filling method. The stage filling method has high production efficiency and good safety. However, the filling body on both sides of the column can be self-supporting and not collapsed. The filling body of the mining area cannot meet the requirements. Therefore, the lining filling method should only be adopted by the lining filling method, combined with the actual site. This time, the selection of the road expansion and recovery mining zone filling scheme (Scheme 1-1) and the advancement of the upstream road expansion and recovery mining zone filling scheme (Scheme 1-2).
3.1 Road expansion and recovery mining partition filling scheme
(1) Arrangement of the stope. The stope layout is divided into a strike direction and a vertical direction. When the vertical direction is arranged, the length of the stope is the thickness of the ore body and the width is the width of the pillar. When the course is arranged along the strike, the length of the stope is the same as that of the first step, and the width of the stop is the width of the pillar. The stage height is 50m (see Figure 1).

(2) Precision cutting. The main mining projects are the middle section of transportation lanes, filling and ventilation patios, and upper and middle sections of ventilation and flat roads. First, in the upper and middle sections, the horizontal transport lanes and the ventilation flats are excavated into the pillars, and then the pits are connected to the upper and middle sections in the pillars. The following middle section of the transportation lane forms a bottom layer for the free surface and the working space, and then a artificial false lane is set up on the bottom of the bottom, and a downhole and a dewatering well are set up along with the mining. If there is a chute available outside the pulse, it is also possible to set up a downhole. The pillar mining can use the original prospecting veins, patios and auxiliary wear, without adding new engineering quantities.
(3) Recovery. The pillars are harvested from the bottom to the top. Firstly, starting from the contact road entering the stope, along the direction of the stope strength, the road is excavated in the center of the stope. When the stratified mining is carried out, the air-leg rock drill is used to drill shallow eyes, and the tunnel is expanded in the approach. The ore is discharged by electric shovel or artificially mined. In order to ensure the safety of the mining operation, a top cover layer with a thickness of about 2 m should be left to the uppermost layer and not recovered as a permanent loss. When stratified expansion and recovery, leave a mine wall with a thickness of about 1m.
(4) Filling. According to the stability of the top plate, multiple filling or layering filling is adopted in the partition, and the filling sand-sand ratio is 1:10. Ventilation in the stope. The fresh air flow enters the working face from the middle section of the transportation lane, the artificial false alley in the pillar, and the smoothing patio. The sewage is discharged to the upper middle section of the return roadway through the filling well.
3.2 Advance upward approach expansion and recovery mining partition filling scheme
The advancing up-and-out approach to the expansion and recovery of the zone filling scheme and the roadway expansion and recovery mining zone filling scheme are basically the same in the stope layout, the mining and cutting engineering, the mining process and the filling process. The main difference is that the upper stratified approach is formed in advance. The super forward path is used as a lower layer filling and ventilation tunnel, as shown in Figure 2.

3.3 program comparison
The technical and economic comparison of the two types of inter-column mining schemes is shown in Table 1.

Compared with the road expansion and recovery mining area filling scheme (Scheme 1-1), each stratified mining system has reduced the amount of minerals in one stratification. The number of depletion of ore is reduced, and the depletion rate is reduced. At the same time, the advancement of the approach can be formed by the topping. Compared with the excavation, the work efficiency is higher and the cost is lower. Moreover, the super forward path formed can be The use of filling and ventilation can avoid the single working face of the tunneling and the ventilation effect is better. When filling, the filling pipe can be installed in the super forward road to facilitate the filling operation, which is easy to control during filling and is suitable for filling the roof. If the filling is sufficient, the height of the empty top of the goaf can be reduced, which is conducive to safe operation.
4 top bottom column recovery plan selection
4.1 Straight wall approach filling continuous recovery plan (Scheme 2-1)
(1) Arrangement of the stope. The approach of the vertical ore body of the scheme is to arrange the length of the ore body. The length of the approach is the thickness of the ore body. The span is based on the stability of the ore body. The conditions of the ore-bearing backfill are 2 to 2.5. 5m, high 2 ~ 2.5m, as shown in Figure 3.

(2) Precision cutting. The main mining projects include middle section transportation lanes, pedestrian ventilation shafts, slip mines, contact roads, layered alleys, and upper and middle sections of ventilation and flat roads. First, the manhole ventilation wells and the sloping mines are dug in the columns between the two ends of the mining area, and the upper and middle sections are communicated, and then the tunnels and stratified roadways are traversed along the ore body. As each exploration line has been arranged with prospecting veins, patios and auxiliary wear. Therefore, if the pillar is located in the exploration line, the well and the pedestrian ventilation well can use the original prospecting project without adding new engineering quantities.
(3) Recovery. The top and bottom columns are stratified from the bottom to the top. Each layer of mining starts from the stratified roadway, and the vertical direction approaches the continuous retreat. The access section (2.0×2.5) m～(2.5 ×3.5)m.
After each approach is finished, it is filled with graded tailings. Except for the first recovery tunnel, each side of the approach is a cemented fill and one side is a mine wall. In order to improve the stability of the filling body and reduce the loss of depletion, the side of the mineral wall is designed as an inclined wall of about 70° to 80° to form an inclined wall approach. The top and bottom columns are backed with a 2m thick roofing layer. The ore is discharged or discharged manually.
(4) Filling. After mining to the boundary, a water filter retaining wall is installed at the entrance, and then filled. The filling is filled with a graded tailings cement, and the ratio of sand to sand is 1:6 to 1:8.
(5) Ventilation of the stope. The fresh air flow is entered by the middle section of the transportation lane, the pedestrian ventilation shaft, the contact road, and the layered roadway. The sewage is passed from the other side ventilation shaft to the upper middle return air passage. When the working face of the approaching mining is a single working face, the auxiliary fan ventilation is required.
4.2 Two-step approach filling interval recovery scheme (Scheme 2-2)
The two-step approach filling interval mining scheme and the inclined wall approach filling continuous mining scheme are basically the same in the stope layout, the mining cutting project, the mining process and the filling process. The approach adopts step-by-step interval recovery, the first step is post-harvest cementation filling, the ratio of sand to sand is 1:6～1:8; the second step is non-cemented filling after recovery, the ratio of sand to sand is 1:10～1:12, such as Figure 4 shows.

4.3 program comparison
The technical and economic comparison of the two top and bottom column recovery schemes is shown in Table 2. For the recovery of the top and bottom columns, both schemes can achieve the maximum ore recovery rate, but the inclined wall approach fills the continuous mining top and bottom column scheme with less working surface and less production capacity, which makes it difficult to increase the recovery strength. The extension of the mining time will have an adverse impact on the safe production. At the same time, in the recovery of each approach, the access side is the ore body and the side is the filling body. To ensure the safety of the recovery, the depletion loss index is reduced. The filling quality requirements are higher, the filling cost is correspondingly increased, and the two-step approach filling interval recovery scheme is better.

(1) Through the research and comparison of the mining schemes of the inter-column and the top-bottom column, through the field test, the inter-column adopts the advanced upward approach to expand the mining area partition filling scheme and the top-bottom column adopts the two-step approach filling interval recovery scheme. Technically feasible, good economic and technical indicators can be achieved.
(2) In order to ensure the safety of the entire pillar mining, and save the mining project, the mining sequence of the pillar should be the first mining bottom column and the rear mining column.

(3) Safety measures should be taken during the promotion. When adopting the advanced upward approach and expanding the mining area filling scheme to recover the middle section column, it is necessary to reduce the exposed area and exposure time of the roof of the ore body, strengthen the roof management and timely fill.
references:
[1] Editorial Board of Mining Design Handbook. Mining Design Manual [M]. Beijing: China Building Industry Press, 1986.
[2] Yan Hongtao. Current status and countermeasures of mining pillars in non-ferrous metal mines in China [J]. China Mine Engineering, 1992 (2): 14-18.
[3] Changsha Mining Research Institute Co., Ltd. Research on safe mining technology of pillars under the condition of poor cemented backfill [R]. Changsha: Changsha Mining Research Institute Co., Ltd., 2008.
[4] Yu Runcang. Mining Engineer's Handbook [M]. Beijing: Metallurgical Industry Press, 2009.